Low density granular or powder explosives and their manufacture



Patented Oct. 22.1%46

2 cans deterrence LOW DENSITY GRANULAR OR POWDER EXPLOSIVES AND THEIRMANUFAC- John Whetstone, West Kilbride, Scotland, assignor to imperialChemical Industries Limited, a corporation of Great Britain No Drawing.Application September 19, 1942, Se-

rial N0. 458,993. 15, 1941 '9 Claims. 1

The present invention relates to granular detonating explosivecompositions of the kind in which the granules individually compriseammonium nitrate and aneasily fusible .organic explosive compound in astate of intimate admixture. The invention relates more particularly tothe provision of new or improved granular explosive compositions asaforesaid that have low density characteristics, and to an improvedprocess for the production of low density granular explosives suitablefor commercial blasting purposes.

Blasting explosive powders containing ammonium nitrate and organicexplosive compounds are :usually manufactured by grinding the solidammonium nitrate and the organic explosive togethen even when, as in thecase of fusible aromatic nitro-compounds such as TNT, the organicexplosive compound is easily fusible. Any additional ingredients of thecomposition are introduced during or subsequent to the grindingoperation. Prolonged grinding is required inorder'to produce anexplosive satisfactorily sensitive to initiation by a. commercial,detonator. Granulated compositions made from the resulting powclersordinarily show a bulk density of about-0.9 to 1.15 grams, percubic'centimetre when car- .tridged under a pressure of 75 lbs persquare inch.

Low density ammonium nitrate blasting explosive powdersof the kind inwhich the low-density ,is not occasioned by the useof low densityvegetable tissue, vonthe contrary, are made by lightly mixing ammoniumnitrate crystal aggregates .of vlow density with the solid oxidisableingredient's. The low density ammonium nitrate crystal aggregatesfacilitate the attainment of a composition initially sensitive todetonation, but must not be .brokendown, and low density blastingpowders of this kind frequently suffer from the defect that the granulesconstituting them are .so .fragile that they disintegrate .very easilyWhenjostled, egg. .in transport, or on storage, and

thereby .become denser and less sensitive.

Military explosives containing ammonium nitrate and aromaticnitro-compoundscan be made bycoating solid ammonium nitrate with thefused aromaticv nitro-compound,-the explosive compositions so obtainedbeing compressed; or cast, or cast and compressed into the ammunition inwhich they are to be used. They are, however, seldom sensitive toinitiation by ordinary detonators, and in reflecting their detonation itis necessary to employ an intermediate primer or booster whereby thedetonating impulse transmitted from thedetonatoris enhanced. Thedensity'of-such charges usua1ly exceeds 1.4 and their ii w e In GreatBritain September velocity of detonation and their negative oxygenbalance are usually higher than is desirable for commercial blastingpurposes.

:The fusion temperature of ammon um nitrate is too high to enable it tobe safely melted With fusible or anic xpl sive co p ds. u it an bereduced by the inclusion of additional materials such as salts havingWater of crystallisation, and by vari us alts an or a i materials that.fo m t cti mix ures with it. In t ma ufac- .ture of mstfiXpMsW charges.such materials, usually pf a xid s n or ,reducina i aracter, e be nincluded .in molten compo it ons co ins ammonium nitrate and organicexplosive poun s. w th th object of minim sing the ontent of the org niexplcsire compound required o y eld a c pos t on that can c eniently beloaded. These compositions containing ammonium nitrate in a more or lesscompletely fused condition, however, suffer from the defect that the Jgu fied ino anic salts and e molten organic explosive constitute twoimmiscible liquids tha a on vheco sc y dispersed bya itamom-9thelngeltso tha the s lt n ixtu e celie ate ap dly heter it olidifies.and the reult g cas exp os ve char es are of lower se itivene s toi itation than those made by oating the solid oxidising salts with moltenorganic explosive and ,mayfail to propagate their detonaonpmn r y- 1 11th p eparatio of cast e pl s v char such as arel sedfor fillingcontainers, for example shells or other projectiles, grenades, ,minesand the'likch thas been .pr posedto emu s fy with th aid ofanflmulsifyingagent a highlyexplosive organic compound .or compounds ina .melt of an oxidising salt or salts, for instance ammonium nitratewith or without metallic nitrates. Accordingto this proposal, theemulsifying agent maybe a, colloidal substance soluble or swellable bywater .a-ndcapable of increasing the viscosity of the melt,andthe-formation of the saline melt into which the highexplosiveorganic'compound, for instance TNT, is incorporated, may be assisted bythe presence of ahydrated salt, an organic' amidegor a small proportionof water, "the resulting emulsified explosives jbeing characterised byimproved sensitiveness to detonation and other advantages as comparedwith similar com positions made .by.a fusion process or partial fusiOn.process without the use of the emulsifying agent. ,one vof theseadvantages is that compositions of sulflficientjfluidity for loadinginto ammunition may be obtained at safe workingtem- SEEM till llUUru 3peratures, e. g. 80 to 110 C., with a reduced proportion of the fusiblehigh explosive compound.

Massive cast explosive charges produced according to the method of theaforementioned proposal, however, are insufficiently sensitive to beinitiated by an ordinary commercial detonator. and are unsuitable forcommercial blasting purposes.

It is an object of the invention to provide granular low densityammonium nitrate explosives by a fusion process employing molten fusibleorganic explosive compounds, which will be of suitably highsensitiveness to initiation for commercial blasting purposes, but whichwill be free from the aforesaid defects of the hitherto known lowdensity explosives made from ammonium nitrate and solid organicexplosives or other oxi disable ingredient of ordinary density.

According to the present invention, in the manufacture of detonatingexposives suitable for commercial blasting purposes, a molten easilyfusible organic explosive is emulsified, with the assistance of anemulsifying agent, in an aqueous medium that comprises a saturatedsolution of ammonium nitrate carrying solid ammonium nitrate insuspension and free from readily hydratable salts, this medium beingadapted to yield a pourable emulsion at the emulsification temperature;th resulting aqueous emulsion is congealed into solid form and convertedinto granules, and the resulting granules are subsequently dried at atemperature insuflicient to cause them to soften.

According to another feature of the invention, the grist of the granuleis made more uniform by screening them, and according to a furtherfeature of the invention at least the fine material rejected as a resultof the screening operation is remelted to form a portion of the pourableemulsion that is congealed and converted into granules in a subsequentpreparation.

In putting the invention into efiect, there may advantageously beemployed solid high explosive compounds melting at temperatures notappreciably in excess of the boiling point of water, but which willremain solid under ordinary hot storage conditions, for instancetrinitrotoluene, tetranitroanisol and dinitrobenzene; but there may alsobe employed mixtures containing high explosives of higher meltingpoints, for example, hexanitrodiphenylamine, pentaerythritetetranitrate, polynitronaphthalenes or the like, with easily fusible oreven liquid explosive compositions in suitable proportions to yieldmixtures that will be solid at hot storage temperatures but liquify attemperatures not substantially above the boiling point of water. It isusually convenient to carry out the emulsification at a temperaturebetween about 80 and 110 C.

As emulsifying agents there are advantageously employed colloidalsubstances j soluble or swellable by water and capable of increasing theviscosity of the hot aqueous ammonium nitrate solution, for instanceagar-agar, sodium alginate', carrageen moss extract, flour, dextrin,sodium cellulos glycolate, starch and Various gums. The quantity of theemulsifying agent required will usually liebetween 0.3 per cent and 0.7per cent of the dry weight of the emulsion. The emulsification may beassisted by agitation.

If desired, ingredients of various types commonly employed in themanufacture of explosive compositions may be introduced into thecomposition of the emulsion, in which case they are preferably of aninsoluble and infusible typel. Cooling or quenching ingredients such asfluorspar, dolomite, or anhydrite, or oxidisable ingredients such asmetal powders may thus be introduced. Fusible or soluble materials,however, can often be employed provided they do not have the property ofreadily forming hydrates with water of crystallisation and are notunduly hygroscopic. Examples of salts that may be employed in this wayinclude sodium chloride and sodium nitrate. Ingredients commonly used inblasting explosive l compositions, for instance carbonaceousingredients, especially those of low density, cooling or flame-quenchingagents, waterproofing agents; oxidising salts; noncarbonaceousoxidisable ingredients and so forth may also, if desired, be used inadmixture with the granules obtained after the emulsion has beencongealed and granulated, advan tageously after they have been dried. Insome cases they may be applied as surface coats to the dried granules.It will be understood that the composition of the final explosive shouldbe so adjusted that it has a desirable oxygen balance, taking intoaccount any wrapping or packing material that will be included in theblasting charge. It is noteworthy that if sufiicient water were includedin the composition to dissolve the whole of the ammonium nitrate at atemperature suitable for emulsification, the emulsion would not congealsatisfactorily when subsequently cooled, so that the granulation of theproduct would be impracticable. Although the fluidity of the ammoniumnitrate and of the emulsion as a whole at the emulsification temperatureis somewhat influenced by the nature and amount of the other non-aqueousingredient or ingredients, we have found that in the case of a blastingexplosive composition consisting of trinitrotoluene, ammonium nitrateand an emulsifying agent about 3 to 8 per cent. water should be present,so that about 30 to 60 per cent. of the ammonium nitrate remainsundissolved at th emulsification temperature.

The granulation may be carried out by pouring the emulsion into the formof an extended cake or the like, and breaking up the latter mechanicallyinto granules when it has congealed. Any particles that are too large ortoo small may be screened off before or after the granules have beendried off.

The waste from the screening operation may be utilised in forminganother batch of emulsion, advantageously with the addition of a littlewater, since a certain amount of drying may have taken place by the timethe congealed granules have been screened. The size of the granules maybe controlled by varying the intensity of the mechanical action inbreaking up the congealed cake. The bulk density of the resultingexplosive depends amongst other factors on the sizeof the granules, butit will be understood that the invention includes not only explosivecompositions of coarsely granular form, but also explosive com positionsin which the granules are small, and

which may be described as powders.

The granular explosives made according to the present invention arecharacterised by possessing desirably low density characteristics, butthe granules of which they are composed are nevertheless of a robustcharacter which enables them to maintain their desirably low densitycharacteristics during transport and storage. These explosives alsopossess other desirable properties,

more particularly, excellent or improved sensi tiveness to initiationand low velocity of detonation. They may be used in quarrying or miningDZ. tJJ LUDWE, I llluw LUiiHrv DKUDD KU'LKEHUE low densitycharacteristics for use in situations where it is desired to break upthe material to be blasted without efiecting an intensive degree ofcomminution, for instance in the winning of lump .coal. They maintaintheir solidity and low density at the climatic storage temperatures usedin testing. Y The unusually low density characteristics of theexplosives of the present invention, however, are due not only to thegranulation of the congealed emulsion, but also to the evaporationofwater from the individual solid granules. In drying the granules,therefore, the temperature must not be sufficient to cause incipientfusion of the granules, which would destroy the desired porosity, but asthe drying proceeds the drying temperature may, if desired, beprogressively increased.

The dried granules may advantageously be pro vided with a coating of awaterproof material, but this is not essential. They should be packed inwaterproof containers, and if the granules have not been coated it isoften desirable that they should be packed in containers which willresist the entry of water vapour. It is desirable that the explosiveshould contain no ingredient of a marked deliquescent character.

When cooling and flame-quenching ingredients are included, explosives ofsuitable composition for blasting in fiery or gassy mines may also bemade in accordance with the presentinvention.

The invention is further illustrated by the following examples, in whichthe parts are parts b weight.

Example 1 A mixture of 81.5 parts ammonium nitrate, 6 parts water and.0.5 part agar-agar are heated until the agar-agar has dissolved and thetemperature has risen to 81 to 85 C. 18 parts trinitrotoluene arestirred in and the mixture is further heated to 90 C., by which time thetrinitrotoluene has melted, and is stirreduntil 'a well dispersedpourable emulsion has been formed. The aqueous emulsion is then-pouredon to a cold surface to form a slab of about A inch in thickness, whichis crushed into granules after it has congealed, and is screened. Theparti-' cles passing a No. 16 and retained by a No. 25 B. S. sieve arethen dried off at 35 to 45 C. The resulting explosive when cooled andcartridged under a pressure of 75 lbs. per square inch has a bulkdensity of 0.7. The explosive has a power amounting to about 85 percent. of that of blasting gelatine, reckoned on a weight basis. The,explosive when initiated by a No. 6 mercury fulminate potassium chloratedetonator has a velocity of detonation of about 2400 metres per second.

Example 2' The procedure is the same as in Example 1, except that thecake of congealed aqueous emulsion is broken up into smaller particlesand after these have been dried they are screened through a 25 B. S. S.sieve, all the coarser material being appropriately sized to provide amore coarsely granular explosive. The material passing the 25 mesh sievewhen cartridged at a pressure of 75 lbs. per square inch in a, waxedpaper cartridge has a density of 0.8 and detonates under the impulse ofa No. 6 mercury fulminate-potassium chlorate detonator at a velocity ofabout 2,900 metres per second. In a test in which two 1%" x 3" freshlymade cartridges of the same explosive in their waxed paper wrappers areplaced in line at, varying distances in a common paper wrapper, thesecond cartridge is detonated by the first at a distance of 4" but notat 5".

Ea'ample 3 Amixture of 73.4 part ammonium nitrate, 5 parts water,and 0.4part agar-agar are warmed until the agar-agar has dissolved and thetemperature has risen to 85 C. 16.2 parts trinitrotoluene are'stirred inand the mixture is further heated to 90 C. and agitated until the moltentrinitrotoluene has been emulsified. parts anhydrite, screened to pass a40 mesh sieve and to be retained on a 60 mesh B. S. Sieve, are

tated. The mixture is then poured on to a cold surface to form a slab ofabout 4" thickness and crushed into small granules after it hascongealed. It is dried and screened to pass a mesh B. S. sieve, and thelarger particles retained on the sieve are sent for remelting. Whencartridged in waxed paper tubes at a bulk density of 0.8 the resultingexplosive detonates under the impulse of a No. 6 mercuryfulminate-potassium chlorate detonator at a velocity of 2200 metres persecond. Its power is about 71 per cent. of that of blasting gelatine. Inthe double cartridge test described in Example 2 the second cartridgewas detonated by the first at 3" but not at 4". 7

Example 4 The procedure is the same as that of Example 3 except thattalc is used in place of anhydrite. The properties of the explosive aregenerally similar to that of Example 3.

Example '5 The procedure is the same as in Example 3 except thatfiuorspar is used instead of anhydrite. The properties of the explosiveare generally similar to that of Example 3.

Example 6 The procedure is the same as that of Example 3 except thatlimestone, screened to pass a mesh sieve but not to be retained one. 100'mesh' 60 Example 7 The explosive is prepared as described in Example 3,except that the proportions of ingreclients employed are as follows:ammonium nitrate 69.6 parts, agar-agar 0.4 part, water 5 parts,aluminium 15.0 parts, trinitrotoluene 15 parts. The bulk density of theexplosive when cartridged under a pressure of 75 lbs. per square inch isabout 0.75, and the explosive is initiated under the impulse of a No. 6fulminate-potassium chlorate detonator with a velocity of about 2300metres per second. The power of the explosive is about 90 per cent. thatof blasting gelatine. An explosive of similar composition made bymilling together the dry ingredients has a density under the samecartridging pressure of about 1.1 and 23876155!!! lluunv then stirredinto the mixture which is kept agidetonates. with a velocity of 3600:metres per second.

l Example 8 The explosive is prepared according to the method of Example3- except that sodium chloride isfusedinstead oi anhydrite, and theproportions oi, the. ingredients: used are-ammonium nitrate 71.6 parts,sodium chloride. 13 parts, Water 4 parts, agar-agar 0.4 part andtrinitrotoluene 15 parts. Under a cartridging pressure of 75 lbs. persquare inch the bulk density of the dried granules is about 0.9, and under the impulse. of a No. 6 mercury fulminate-potassium chloratedetonator, the resulting explosive detonates with a velocity of 2200metres per second. An explosive of similar composition made by a. drymilling process when cartridged under the samepressure has a density ofabout 1.1 and a velocity of detonation of about 3500 metres per second.

Example 9 The ingredients used for making the explosive are 'thesame asin Example 8, but the sodium chlo'ride'is mixed with the dried granulesof the solidified emulsion containing only the. ammonium nitrate,agar-agar and trinitrotoluene instead-of being included in thecomposition of the aqueous emulsion. The sodium chloride is employed incrystalline form passing a 40 mesh and retained by a 60 mesh 13. S. S.sieve. Under acartridging pressure of 75 lbs. per square inch thedensity is about 0.9,. and the velocity of detonation is about 2600metres per second under the impulse of a No. 6 mercuryfulminate-potassium chlorate detonator. In the double cartridge test thesecond cartridge is initiated by the first at 4" distance but not at 1While in the preceding examples there is illustrated the use of a- No. 6mercury fulminatepotassium chlorate detonator, all of these explosiveswhen freshly made are capable of being initiated by a No. 2 mercuryfulminate-potassium chlorate detonator. The hereinbefore quotednumerical values for bulk density are reckoned on" the basis that thebulk density of water is unity,

. 8 I claim:

l. A process for the manufacture of low" density blasting explosiveswhich comprises emulsifying a molten easily fusible organic explosivewith the assistance of an emulsifying agent in an aqueous medium thatcomprises a saturated solution of ammonium nitrate carrying solidammonium nitrate in suspension and is free from readily hydratablesalts, this medium being adapted to yield a pourable emulsion at theemulsification temperature, congealing and granulating the resultingaqueous emulsion and drying the resulting granules. at a temperatureinsufficient to cause them. to soften.

2. A process as. claimed in claim 1 wherein the granulation is carriedout by pouring the emulsion into the form. of an extended cake or thelike and breaking up the latter mechanically when it has congealed.

3; A processas claimed in claim 1 wherein the fusible: organic explosivecomprises an explosive compound melting at a temperature notsubstantially exceeding the. boiling point of Water.

4. A process as claimed in. claim 1 wherein the fusible explosivecomprises a mixture of compounds thatv fuses at a temperature notsubstantially exceeding the. boiling point. of water, of which oneconstituent is a compound melting at a temperature substantiallyexceeding the boiling point of water;

. 5. A process as claimed in claim 1 wherein the fusible. explosivecomprises trinitrotoluene.

6. A process as claimed in claim 1 wherein the emulsificatio-n iscarried out at a temperature between C. and1l0 C.

7. A process. as claimed in claim, 1 wherein the quantity of emulsifyingagent employed amounts .to from 0.3 to 0.7 per cent. of the dry weight.of the emulsion.

8... Av process as claimed in claim 1 wherein the emulsion consists of amixture. of ammonium nitrate, trinitrotol-uene, an emulsifying agent andfrom 3 to 8. per cent. of water reckoned on the weight. of the emulsion.

- 9.. A process as claimed in claim 1 wherein the ammonium nitratecomposition contains a metal powder.

JOHN WHETSTONE.

